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Number 193 ' July 1, 1970 


By William J. Morris 

Los Angeles County Museum of Natural History • Exposition Park 
Los Angeles, California 90007 

CONTRIBUTIONS IN SCIENCE is a series of miscellaneous technical papers 
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Robert J. Lavenberg 
Managing Editor 


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Virginia D. Miller 


By William J. Morris^ 

Abstract: Reconsideration of the morphology and function 
of the bill of hadrosaurian dinosaurs is based upon an excellently 
preserved bill mold of a recently discovered specimen (LACM 
23502) assigned to the genus Anatosaurus. Morphology suggests 
a filtering function for the bill and adaptation for discharge of 
fluid and small particles following intake and mastication of plant 
or invertebrate food. 


The excellent specimen of Anatosaurus cf. annectens (LACM 23502) 
upon which this study is based was discovered and collected by H. Garbani 
and skillfully prepared by M. Odano, both of the Los Angeles County Museum 
of Natural History. The skeleton was found in the Hell Creek Formation south 
of Ft. Peck Reservoir, NE V4 , Sec. 36, T21N, R35E, Montana. 

The project, leading to this discovery as well as other important dinosaur 
finds, was generously supported by Mr. and Mrs. William T. Sesnon, Jr., 
patrons of the Los Angeles County Museum of Natural History. 

Constructive criticism of the manuscript by Dale Russell, Canadian 
National Museum, and Theodore Downs of the Los Angeles County Museum 
of Natural History is appreciated. Others on the staff of the Los Angeles County 
Museum whose help is acknowledged are: David Forstch and Alan Tabrum 
for their interest and discussion, and Joseph Cocke for his drawing of Figure 2. 
The remainder of the illustrations and photographs were done by the author. 

Dinosaurs of the family Hadrosauridae are among the most familiar Late 
Cretaceous fossils. Indeed, the first dinosaurs described from North America, 
belonged to these so called duckbilled forms. Prior to a brief description by 
Cope (1883) the presence of a horny bill in hadrosaurs was conjectural. Cope, 
in preparing a specimen of Anatosaurus annectens, discovered portions of a 
mold of the bill. Later two other specimens in which most of the bill was 
preserved were described for A. annectens by Versluys (1923) and for 
Corythosaurus excavatus by Sternberg (1935). In all three cases we must rely 
upon the description of the bill as the original molds were either destroyed 
during preparation or subsequently lost. As a result, a recently discovered 
specimen of Anatosaurs cf. annectens (LACM 23502) from the Hell Creek 
beds of Montana containing a well preserved mold is most important in 

"Research Associate in Vertebrate Paleontology, Los Angeles County Museum of 
Natural History; and Professor of Geology, Occidental College, Los Angeles, 
California 90041. 



Hadrosaurian Dinosaur Bills 

Contributions in Science 

No. 193 

?■■: ^1 




2 Contributions in Science No. 193 

evaluating the morphology and function of the hadrosaurian bill. The letter 
designations are used to designate specimens in various museums: LACM, 
Los Angeles County Museum of Natural History; ROM, Royal Ontario 
Museum; NMC, National Museum of Natural Sciences, Ottawa. 

Bill Morphology of Anatosaurus cf. A. ANNECTENS (LACM 23502) 

The specimen is a mature individual approximately forty feet long. The 
skull is only slightly distorted mainly along a parasagittal section approximately 
midway between the orbits and narial openings. The mandibles, though offset 
to the right, are not distorted relative to the midline so that the bill mold is 
undistorted, (Fig. 1). Morphologically, the specimen is very similar to 
A. annectens but there are some differences between it and the holotype. Until 
the time when careful study has been made regarding individual variability of 
hadrosaurian dinosaurs, it is hazardous to make positive, specific references for 
specimens other than the type. This is especially true regarding the LACM 
specimen for it was found further north than the Lance Formation, Wyoming, 
localities from which the types of A. annectens were obtained. 

The bill mold is composed of gray, lithic siltstone, the surface is accentu- 
ated by a thin veneer of iron oxide. In the figures, the mold appears dark due to 
the application of preservative although it has the same composition as the 
matrix. The entire anterior surface (attached dorsally to the premaxillary 
region) is preserved and only a small portion of the ventral edge is lacking. 
Only the left side is preserved. 

Before discussing the form and function of the bill it is important to 
describe the geometry of the mold. Errors in interpretation by other authors 
seems largely to have resulted from misinterpretation of the geometry of the 

When the specimen was discovered, anterior and posterior sides of the 
mold were preserved with a very thin surface of weakness separating them. The 
surface, shown in Figures 1, A, B, C and D, is the posterior side of the mold, 
the one closest to the premaxillary region of the skull. It is important to note 
that matrix on both sides of the preserved surface was carefully prepared and 
other structures were not found within the matrix except the surface of the 
mold. Hence the entire bill, as preserved, is represented by two surfaces 
separated by less than 0.01 mm, one of which is shown in the figures. 

The surface of the mold is vertically fluted, containing nine or possibly 
ten V-shaped channels. These are separated by dorsal-ventral pillars, rounded 

Figure 1. Partially prepared skull of Anatosaurus cf. annectens, LACM 23502. 

(A) Complete skull, left side. The bill mold is not preserved on this side but the 
edge of the mold can be seen extending ventrally from the premaxillary below the 
predentary of the lower mandible. Note that the free margin of the mold extends 
below the predentary and is separated from the predentary by siltstone matrix. 

(B) Anterior undulating surface of the bill mold showing the fluted channels 
preserved as an iron oxide veneer on the siltstone matrix. (C) Dorsal oblique 
aspect of the skull illustrating the very terminal position of the bill mold along 
the ventral margin of the premaxillary. (D) Ventral oblique view showing the 
bill mold and the matrix layer separating it from the predentary. 


Hadrosaurian Dinosaur Bills 

in cross section. Laterally, towards the maxillaries, the fluted surface is re- 
placed by a smooth triangular plate. 

The mold is approximately 110 mm long at the junction of the pre- 
maxillaries and it extends ventrally about 50 mm below the anterior margin 
of the predentary, decidedly overlapping the front of the lower jaw. Although 
the extreme ventral margin of the mold appears to be missing, the taper of the 
pillars and channels suggests that the entire bill was not much longer than 
shown in this specimen. 

The premaxillary of the specimen, dorsal to the mold on the left side, 
is not well preserved and the surface separating bill and upper jaw cannot be 
seen. There is, however, little doubt that the bill was united with the upper 
mandible. A complimentary structure that would have been attached to the 
lower mandible was not found even though conditions for its preservation must 
have been similar to those for the upper bill mold. 

Interpretive Morphology 

The surface of the mold forms an immediate extension of the pre- 
maxillary without break or offset. The actual horny bill must have been 
affixed anterior to the mold and, in order to be secure, must have extended up 
and onto the surface of the premaxillaries. Although there is no direct evidence 
indicating the posterior limit of the bill, it probably did not extend farther than 
the excavation surrounding the nares in the premaxillaries. 

The geometry suggested by the anterior position of the mold suggests that 
the mold reflects the interior surface of the bill. Probably some compression 
of the bill occurred during compaction of the silt now forming the matrix, and 

Figure 2. Restoration of the bill on the skull of Anatosaurus of. annectens, LACM 
23502. The undulating, fluted inner surface of the bill is shown. When the mandibles 
were closed and the predentary opposed to the bill, channels opening from the 
mouth were formed. 

6 Contributions in Science No. 193 

it is impossible to determine the original thickness of the specimen. The fluted 
surface was evidently confined to the interior of the bill as no comparable 
surface was found against the more dorsal surfaces of the premaxillary. Con- 
ceivably the original exterior fluting could have been destroyed during com- 
paction but then why was it not also destroyed on the more ventral portion? 
It seems best to reconstruct a bill with the fluted surface only on the internal 

The predentary is poorly preserved and furnishes no evidence for a bill on 
the lower jaw. Nor was evidence for the presence of a lower bill found in the 
matrix anterior to the predentary. 

A restoration of the probable appearance of the upper bill is shown in 
Figure 5. 

Discussion of Previously Described Bill Molds 

The specimen described by Cope was destroyed during preparation of 
the skull. Cope did not give a reason for destroying the mold, but one cannot 
help conjecturing that he thought his description vivid enough that future 
reference to the specimen would be unnecessary. The mold of the Cory- 
thosaurus excavatus specimen, except for a very small and unilluminating 
fragment, could not be located. In the third example Versluys apparently used 
the mold to cast what he took to be a plaster replica of the bill and, after 
obtaining the cast, the natural mold was not retained. 

Cope appears to have misinterpreted a structure very similar to that of 
LACM 23502. The full text follows (1883: 106) : "Dermal or corneous struc- 
tures have left distinct traces in the soft matrix about the end of the beak-like 
muzzle. Laminae of brown remnants of organic structures were exposed in 
removing the matrix. One of these extends as a broad vertical band round the 
sides, indicating a vertical rim to the lower jaw, like that which surrounds some 
tea trays, and which probably represents the tomia of the horny sheath of a 
bird's beak. At the front of the muzzle its face is sharply undulate, presenting 
the appearance of vertical columns with tooth-like apices. Corresponding 
tooth-like processes, of much smaller size, alternate with them from the upper 
jaw. These probably are the remains of a serration of the extremital part of the 
horny tomia, such as exists on the lateral portions in the lamellirostral birds." 

Cope described an undulatory surface with tooth like terminations; how- 
ever, he did not make it clear whether he considered the object examined a 
mold or the actual bill. He implies that the structure was attached to the lower 
jaw and that only small protuberances were present on the upper. Cope prob- 
ably misinterpreted the area for attachment of the bill, judging from the LACM 
specimen. Versluys (1923) also believed that Cope's analysis was in error, but 
Lufl and Wright (1942) and Ostrom (1961) both accepted Cope's (1883) 
description of a horny beak on the lower jaw. Probably the smaller, tooth like 
processes described by Cope were rugosities normally present distally on most 
hadrosaurian premaxillaries. 

The morphology of the hadrosaurian bill was further confused by Lull 
and Wright who state (1942:43). "In the Senckenherg specimen [the one 

1970 Hadrosaurian Dinosaur Bills 7 

described by Versluys] the impression shows a beak on the upper jaw which 
projected with a free lower border for about 8 cm over the ventral edge of the 
premaxillae. The beak stood vertically, with a regular, undulating surface 
which became smoother towards the sides. Cope described the same wavy 
appearance corresponding and alternating with the tooth-like processes in the 
jaw itself. . . . He [Cope] also described a similar horny beak on the lower jaw." 

Cope of course had not described a wavy appearing structure occurring 
on both jaws, the upper being described as small tooth Hke processes. Ostrom 
(1961:152) apparently agreed with Lull and Wright stating, "Cope (1883), 
however, described beak impressions at the anterior extremities of both the 
upper and lower jaws in a specimen of A. copei {Diclonius mirabilis) ." Yet 
neither LACM 23502 nor the equally well preserved Senckenberg specimen 
give any indication of a lower bill. 

Sternberg figured a bill mold in describing a specimen of C. excavatus 
(NMC 8676) , but in neither the plate explanation nor in the body of the paper 
did he state that the bill was attached to the lower mandible (Fig. 3). Ostrom, 
however, (1961:152) states, "Further evidence of a lower beak has been found 
in a third specimen {Cory thesaurus excavatus) , (NMC 8676), described by 
Charles M. Sternberg (1935), in the form of an impression of an incomplete 
horny beak in front of and along the left side of the predentary." As the plate 
from Sternberg's paper shows (Fig. 3) the mold is a fluted surface associated 
with the lower jaw but it is separated from the predentary by a considerable 
thickness of rock matrix. The presence of matrix between the surface and 
predentary is evidence that the mold is not the opposing surface of a predentary 
sheath. Upon examination of the plate and the small fragment in the collection 
of the Canadian National Museum, it appears as though the mold is that 
portion of the upper bill which originally projected over and in front of the 

Although the fluted surface has been observed on three reported species, 
there is a problem regarding it. Does the fluted surface belong on the external 
surface or the internal surface of the bill? 

Cope, (1883) having interpreted the mold as being attached to the lower 
jaw, apparently assigned the undulatory surface to the exterior of the lower 
bill. On the other hand, Versluys (1923) assigned the undulatory surface to 
the outer surface of the upper bill. Versluys presents excellent drawings show- 
ing that the bill was indeed attached to the upper mandible and that the feature 
is similar to the mold in LACM 23502. However, in reconstructing the bill he 
placed the undulatory surface on the exterior. Versluys removed the posterior 
portion of the bill mold and then poured a substance, probably plaster, against 
the anterior part of the mold, judging from the wording as translated from 
German. The resulting cast was retained but the rest of the mold was not. 
Versluys interpreted this cast as being the bill. He had apparently reproduced 
the posterior part of the original mold formerly occupied by matrix. Such a 
restoration would erroneously cause the undulatory surface to appear on the 
exterior rather than on the interior of the bill. 

Sternberg (1935) did not state whether he believed the undulatory surface 

Contributions in Science 

No. 193 

of the beak to be on the exterior or the interior. Ostrom, however, in discussing 
the specimen of Corythosaurus excavatus described by Sternberg, states, 
(1961:152), "This specimen indicates the presence of small, tooth-like pro- 
jections on the inner surface of the beak, which probably contributed to a firm 
union of this structure with the lower jaw." Sternberg's plate clearly shows a 
layer of matrix between the mold and predentary which is evidence against a 
firm union. In addition, the surface of the predentary, although rugose, is not 
appressed against the mold of the bill and the rugosities do not match the 
channels in the bill mold. 

The various interpretations of the relationship of the undulatory surface 
to the mandibles is illustrated in Figure 4. 

Function of the Hadrosaurian Bill 
Almost every conceivable mode of food gathering has been proposed at 
one time or another for the hadrosaurian dinosaurs. There are no existing 




■J ;■ 


Figure 3. Lower jaw of Corythosaurus excavatus, NMC 8676, showing the bill mold 
(H.B.), predentary (P.D.), and dentary (D). This figure is reproduced from Plate 
II, Sternberg (3). 


Hadrosaurian Dinosaur Bills 


















\ ^ 























Figure 4. Diagram illustrating the interpretations of the four reported hadrosaurian 
bill molds. All interpretations are based upon molds preserved with specimens of 
Anatosaurus annectens except Sternberg (1935) which is based upon Corythosaiirus 
excavatus. Blocks labeled represent the mold as discovered. Block 1 is the posterior 
part of the mold and 2 is the anterior. Blocks labeled B represent the parts of the 
mold preserved after preparation. Block C in the case of the interpretation by 
Versluys represents a plaster cast that was poured against B-2- Each group of blocks 
is followed by the interpretation placed upon them by the authors listed. Lastly, 
outline restorations are shown illustrating the interpretation by each other. 

10 Contributions in Science No. 193 

reptiles that have comparable feeding or masticating features. Cope suggested 
a diet of soft vegetable matter but this was based on the erroneous assumption 
that the teeth, in particular those of the dentary, were only loosely attached. 
Lull and Wright (1942:36) give the following picture, "The analogy now 
seems to be with the moose Alces whose diet is that of a browsing animal, that 
is the twigs and leaves of deciduous trees . . . and also certain conifers. In 
summer it turns to the tall, lush grass in swamps or near the margins of streams 
and lakes and, actually invading the water, feeds upon the leaves of the water 
lily or, with head entirely submerged, on the roots and stems of aquatic 

Versluys strongly rejected the idea of a ducklike feeding habit as reported 
by Abel (1912). Instead, he suggested that the structure was more beak than 
bill adapted for scraping bark and leaves from small scrubs and trees or even 
for the uprooting of plants. 

There is only one report of stomach contents associated with a hadro- 
saurian skeleton. Unidentified plant debris and recognizable conifer needles 
were reported (Krausel, 1922) from the stomach cavity of A. annectens. As 
pointed out by Ostrom (1961), this might indicate merely that these creatures 
could feed on land plants, and it does not eliminate the possibility that they 
fed on aquatic vegetation as well. Indeed, the harsher fibers of land plants 
might be more readily preserved than the softer materials of aquatic plants. 

In any analysis of their feeding habits, several morphological features 
must be taken into account and the assumption made that all of the features 
functioned together in an integrated well adapted system. The hadrosaurians 
were remarkably successful. Not only are their remains relatively common but 
genera have been recognized in North and South America and Eurasia. Despite 
considerable disparity, particularly in the shape of the skull, there are features 
related to feeding habits common to all genera. One is bulk. The probable 
weight of Corythosaurus and Anatosaurus was approximately 4 tons and yet 
the 30 to 40 foot hadrosaurians are not the largest recognized, being surpassed 
by Edmontosaurus and Hypacrosaurus. Small hadrosaurian remains have been 
collected but it is not known if these represent a truly small taxon or are 
immature individuals of the larger species. The few apparently undistorted 
skulls indicate that the hadrosaurians had a constricted buccal passage formed 
by the dentaries and maxillaries, and leading to the throat. In large anatosaurs, 
for example, it is doubtful that particles having a cross-sectional diameter 
larger than three or four inches could have passed along this narrow channel. 
Hadrosaurian dental batteries are very similar, consisting of dozens of teeth 
arranged in closely spaced rows. The occlusional surface is a pavement formed 
of the diamond-shaped crowns of the opposing dental batteries. In addition, in 
all genera three to six teeth are arranged in vertical rows and in each, only the 
most dorsal are in active use. The others serve for a highly effective replace- 
ment mechanism. 

The bill as preserved in LACM 23502, seems to impose certain limiting 
parameters on hadrosaurian feeding habits. The structure seems best adapted 
for filtering. Although several workers have suggested that the bill closed 

1970 Hadrosaurian Dinosaur Bills 11 

against the predentary of the lower jaw forming a cropping device, three 
characteristics of the bill seem to negate this function: 1 ) The bill was attached 
to the anterior and dorsal segment of the premaxillaries and its free edge 
extended well below the anterior dorsal margin of the predentary; 2) The very 
thin space between the anterior and posterior mold suggests that the bill itself 
was a relatively thin structure certainly not well adapted for foraging leaves 
and branches of trees and scrubs; 3) The last feature is the fluted, undulating 
inner surface of the bill which would have little or no function for foraging 
or browsing, and yet seems ideally suited as a filtering device. 

Hadrosaurian dinosaurs, particularly such forms as Corythosaurus and 
Hypacrosaurus, are envisioned as mainly aquatic animals. A filtering device 
would be very important in assuring that these large animals could ingest large 
amounts of concentrated food relatively free of water in a manner similar to 
that of the dabbler ducks, such as Dendrocynga, Anas and Aix. These eury- 
phagus forms have laminations on the inner surface of the dorsal bill which, 
when closed against the ventral bill, form an efficient filtering device. Such an 
interpretation certainly makes the name "duckbill" even more fitting for the 
hadrosaurian dinosaurs than previously supposed. 

With their very efficient food gathering system, the hadrosaurs could take 
in all manner of food including mollusks and small crustaceans as well as 
plant material. In this sense they would, like many ducks, be relatively high 
protein as well as carbohydrate feeders. Plant material as well as more resistant 
invertebrates could be crushed between the broad occlusional surfaces of the 
impressive dental battery. By lowering the anterior part of the head, excess 
water as well as food particles smaller than approximately one cm would drain 
out of the mouth along the channels formed by the fluted bill and the opposing 
predentary. The resulting masticated material, highly concentrated, could then 
be made to flow down the very small passage between the dentaries to the 
stomach simply by raising the head. 

The presence of the fluted bill, multiple grinding surfaces, mechanism 
for continuous replacement of teeth, and a constricted passage formed from 
the bones of the posterior mouth region makes such a feeding habit feasible. 

Ostrom (1964) presents a very thorough compilation of prior hypotheses 
and information regarding the feeding habits of hadrosaurian dinosaurs. In his 
analysis of the paleoecology the conclusions reached vary only in detail from 
those expressed earlier (1961). In summary Ostrom states (1964:995), "Past 
interpretations of hadrosaurian ecology have pictured these animals as pre- 
dominantly aquatic in their habits, living and feeding in swamps, lakes, or 
rivers and making only occasional and limited excursions out on surrounding 
lands. Anatomic evidence, however, contradicts this interpretation, indicating 
instead that the hadrosaurs as highly adept bipeds were primarily terrestrial 
animals. Other anatomic and botanical evidence shows them to have been 
active terrestrial foragers adapted for browsing on the harsher, fibrous, or even 
woody tissues of trees and shrubs." 

The bill, as reconstructed from the mold of LACM 23502, is very thin 
relative to its lateral and vertical extent, and suggests a structurally weak 

12 Contributions in Science No. 193 

feature, too weak to be of use in browsing on fibrous or woody plants. Ostrom 
is in agreement with the conclusions presented here that hadrosaurian dental 
batteries together with a high degree of tooth wear must have been used to 
masticate food of substantial resistance; however, he suggests that this is 
evidence for foraging upon more resistant terrestrial vegetation. Such a dental 
battery could be used just as effectively for mastication of invertebrates. Ostrom 
(1964:987-989) suggests correctly that in the hadrosaurian localities of the 
Edmonton, Belly River, Judith River, Kirkland-Fruitland, Ojo Alamo and 
Lance marginal and aquatic vegetation are relatively rare in the paleoeco- 
systems. This might, of course, be the result of fortuitous preservation, but even 
if truly representative it could be interpreted as evidence that aquatic and 
marginal vegetation was rare in the area where hadrosaurians were abundant, 
a position taken by Ostrom. On the other hand it could also be evidence for 
the needed addition of invertebrates in the hadrosaurian diet. One must keep 
in mind that the rarity of marginal and aquatic vegetation as computed by 
Ostrom is an absolute occurrence affected by all vagaries of preservation, but 
in the dynamics of the ecosystem it is the relative availability of the plants 
compared to the needs of the hadrosaurian that is significant. 

Hadrosaurians were efficient bipeds and as Ostrom indicates (1964:990- 
993) the articular surfaces of the pes and hind limbs, the large fourth tro- 
chanter, ossified sacral tendons, and reduction of the carpus point strongly to 
this conclusion. These characteristics when treated by themselves may well 
suggest a terrestrial habitat but when the specialized nature of the bill is taken 
into consideration an alternative hypothesis seems more fitting. Therefore the 
conclusion that hadrosaurians were either aquatic or shallow water feeders 
seems appropriate. Under these circumstances the bipedalism as well as the 
specialized bill would be adaptively advantageous. In addition such a feeding 
habit would give credence to the more obvious adaptive significance of the 
laterally compressed tail and the probable presence of webbed hind feet, rather 
than to suggest that these characteristics were for protection allowing the 
otherwise defenseless hadrosaurian to retreat to the water when threatened 
(Ostrom, 1964:993-995). 

Restoration of Hadrosaurian Head 
Figures 5, A, B, and C are sketches illustrating the appearance of billed 
hadrosaurian dinosaurs. Evidence of bills have been found in Anatosaurus 
annectens and Corythosaurus excavatus but not in C. intermedius as restored 
in Figure 5C. In the skull of C. intermedius, however, the distal part of the 
dentary is greatly deflected while the maxillaries are not. The paratype skull of 
C. intermedius (ROM 4671) shows this deflection while, in the same skull, 
the tooth rows are occluded in normal position. If the specimen did not have a 
bill on the upper mandible, then there would have been a wide, opened gape 
at the anterior end of the mouth. The restoration of C. intermedius was made 
as this form has the most exaggerated gape of any hadrosaurian, a condition 
which suggests the presence of a bill, although the magnitude of the gape may 
be partly due to accidents of preservation. 


Hadrosaurian Dinosaur Bills 


Figure 5. (A) Restoration of the skull oi Anatosaiirus annectens. 

Figure 5. (B) Restoration of the skull of Corythosaurus excavatus. 


Contributions in Science 

No. 193 

Figure 5. (C) Restoration of the skull of Corythosaurus intermedius. 

Literature Cited 

Abel, O. 1912. Grunziibe der Palaeobiologie der Wirbectiere. Stuttgard, E. 

Schweizerbart's Verlagsbuchhandlung, xvi-708. 
Cope, E. C. 1883. On the characters of the skull of the Hadrosauridae. Acad. Nat. 

Sci. Phila. Pr. 35:97-107. 
Krausel, R. 1922. Die Kaubewegung und Lebenweise von Edmontosaiirus spec, auf 

Grund der mechanischkonstruktiven Analyse, Palaeobiologica 5:409-422. 
Lull, R. S. and Wright, N. E. 1942. Hadrosaurian dinosaurs of North America. 

Special Paper Geol. Soc. Amer. 40:xi-242. 
Ostrom, J. H. 1961. Cranial morphology of the hadrosaurian dinosaurs of North 

America, Amer. Mus. Nat. Hist. Bull. 122(2) :37-186. 
. 1964. A reconsideration of the paleoecology of hadrosaurian dinosaurs, 

Amer. Jour. Sci. 262:975-997. 
Sternberg, C. M. 1935. Hooded hadr'osaurs of the Belly River series of the Upper 

Cretaceous: A comparison with descriptions of new species, Canada, Dept. of 

Mines, Nat. Mus. Bull. 77(52) : 1-37- 
Versluys, J. 1923. Der Schadel des Skelettes von Trachodon annectens im Senken- 

berg — Museum, Abh. Senckenb. Naturf. Ges. 38: 1-19. 

Accepted for publication March 17, 1970